1. Field of the Invention
The invention relates to a dynamic seal assemblage for effecting the sealing of a piston which is axially movable in a cylinder bore under conditions of extremely high pressure and adverse environmental conditions.
2. Summary of the Prior Art
Hydraulic piston and cylinder assemblies find many applications in subterranean wells, particularly for the operation of safety valves. Such assemblies must operate under extreme conditions of pressure and exposure to a corrosive environment created by the well fluids and gases that are always present.
Many seals have been employed utilizing simple elastomeric elements such as O-rings and T-rings. But for a dynamic seal against high pressures on the order of 15,000 psi and higher, these elastomeric seals have not successfully prevented the passage of gases and other fluids around the seals, or failure of the seal due to extrusion of the elastomeric material. In an effort to solve the problem, it has been suggested that metal-to-metal seals be employed for this application. See, for example, U.S. Pat. No. 4,452,310. Metal-to-metal seals have not been satisfactory, because for them to be functional, the spacing between the seal element and the cylinder bore is required to be on the order of 0.0005-inch. This minimal degree of clearance is very difficult and expensive to obtain in the manufacture and assembly of the components. Finely honed surfaces are a necessity. Moreover, it has been observed that sand is generally the downfall of metal-to-metal seals, inasmuch as the cooperating metal surfaces forming the seal are both hard, and then when sand particles get wedged between such surfaces, scratching or galling of the surfaces is bound to occur, thus laying the pattern for future leakage and deterioration of the seal.